Atherosclerosis is a progressive disease of the vascular system whereby atheroma is deposited on the inner walls of blood vessels. Atherosclerosis is a complex, progressive and degenerative condition resulting in the build-up of cholesterol and other obstructive materials, known as plaque, on the walls of the arteries. The accumulation of plaque narrows the interior or lumen of blood vessels, such as arteries, thereby reducing blood flow.
Plaque occurs in several different forms and may be located in many different anatomies throughout the vascular system. Plaque varies in composition, with portions that are hard and brittle, referred to as calcified plaque, and other portions that are fatty or fibrous. Over time atheromatous deposits can become large enough to reduce or occlude blood flow through the vessels, leading to symptoms of low blood flow, such as pain in the legs (on walking or at rest), skin ulcer, angina (at rest or exertional), and other symptoms. To treat this disease and improve or resolve these symptoms it is desirable to restore or improve blood flow through the vessel.
Various means are used to restore or improve blood flow through atheromatous vessels. The atheroma deposits may be displaced by diametrically expanding the vessel by inflating balloons, expanding stents, and other methods. The deposits may be pulverized using lasers and other methods. Atherectemy catheters may also be used to remove atheromatous deposits from the blood vessel.
Many types of atherectomy catheter devices have been proposed, including catheters with rotating burrs, or lasers to photo-dissolve tissue. Other atherectomy catheters have cutting elements that extend through or beyond an opening in the distal end of the catheter to cut tissue or that cut tissue through a side opening or window in the catheter body. Some of these catheters use balloons or other positioning devices to position the cutter adjacent material to be removed.
One catheter design attempts to capture the removed plaque in a collection or storage chamber so that it can be removed from the vessel. In use, the storage or collection location may fill up with excised tissue debris. If the storage or collection location is contained within the catheter body, a cleaning procedure may require the physician to remove the device to empty the collection chamber.
As used in this application the term “distal” refers to a direction away from the operator and the term “proximal” refers to a direction towards the operator. Thus, the handle of the device is located at the “proximal end” and the “distal end” is the end of the device that is inserted first into the vessel. One recent atherectomy catheter, the SILVERHAWK articulated rotating blade atherectomy catheter, (sold by Covidien) has been designed to treat atherosclerotic plaque by excising it from the artery. The SILVERHAWK catheter (features of which are exemplified in U.S. patent application Ser. Nos. 10/027,418; 10/288,559; 10/89,747; and others) uses a rotating blade, a side cutting window through which the blade can be extended, and a hinged nose design which can be controlled to cause the catheter to assume a straight position or an angled position. During the cutting procedure the catheter is in the angled position so the side cutting window and cutting blade can be urged against the vessel wall. The SILVERHAWK catheter is moved distally through the lesion during the cutting procedure. The SILVERHAWK catheter includes a collection chamber located in a distal portion of the catheter nose distal of the cutting window. The cutting blade and cutting window are configured to direct material cut from the vessel wall through the cutting window and into the collection chamber.
In some tissue cutting devices the collection chamber is located proximal of the tissue cutting element. For example, in co-pending U.S. patent application Ser. No. 13/160,044 filed Jun. 14, 2011, the contents of which are incorporated herein by reference in their entirety, an atherectomy catheter having a proximally located collector chamber is disclosed. The catheter includes a side cutting window and a cutting blade configured to extend through the window to cut material from the wall of a vessel at a treatment site as the catheter is pulled proximally through the treatment site. The catheter includes a material collection chamber which is positioned proximally of the cutting window. During use the cutting window is advanced distal to the treatment site, the cutting blade is extended out the window and material is cut from the treatment site by pulling the catheter proximally across the treatment site. In one of the embodiments the drive shaft is provided with auger blades to help transport cut material proximally to the collection chamber.
Although material cutting devices using auger blades to transport cut material, such as the one described above, have been proposed there are design challenges which must be met in order for the devices to function properly in the environment in which they are used. Therefore, there is need for an atherectomy catheter capable of meeting these design challenges.
These and other aspects of the invention will become apparent from the following description of the preferred embodiments, drawings and claims. The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.